We propose to develop a multiple-contact nerve cuff electrode that can be used to activate and to control selectively force production in several muscles sharing a common peripheral nerve trunk. An electrode with these qualities will eliminate many of the problems that impede more wide spread use of neural prostheses for restoration of limb mobility. Although these electrodes are primarily intended for spinal cord injured patients the selective activation properties would make them suitable for other applications involving nerve trunks such as auditory and visual prostheses. The design approach will involve the development of two numerical models. The first model will be used to solve for the intraneural electric field generated by a cuff electrode housing an array of "dot" electrodes. A second model will be developed that stimulates the behavior of a mammalian myelinated axon when the axon is exposed to an extracellular electric field. In combination, these two models will be used to test the effectiveness of a given cuff design in activating motor axons located only in a small region of a large nerve trunk. This is the fundamental requirement for selective control of multiple muscles with a single cuff implant. Cuff electrode designs determined to be effective by this computer based development effort will be constructed and tested in both acute and chronic animal experiments. The emphasis of acute animal testing will be on evaluating prototype cuff designs. The chronic studies will characterize the long-term efficacy, performance, and reliability of the best cuff designs. Measured results will be compared with model predictions. Studies will be carried out to evaluate the electric field scattering effects of encapsulation layers, connective tissue boundaries, and the neural tissue itself; all of this information will be incorporated back into the models to further refine their usefulness for cuff design. The cuff electrodes to be produced by this grant will improve the reliability and capabilities of motor prostheses, greatly reduce the power requirements of implanted stimulators, and simplify the surgical procedures required to implant electrodes for the control of multiple muscles.